Memory devices can be designed and manufactured using numerous, different materials and storage techniques. For example, volatile dynamic memory devices are typically fabricated using storage capacitors. Data is stored by changing the capacitor charge, and data is retrieved by sensing the stored charge. Volatile static memory devices are designed using latch circuits to store data. Non-volatile memory devices, such as flash, use floating gate transistors to store data. Each of the current memory devices suffers from any one or more of the following: high manufacturing costs, high power consumption, operating speed deficiencies, or scalability. As such, different memory designs are being considered to address some of these problems. One type of alternate memory is based on magnetic storage techniques.
Toroidal core memory arrays can be used to store data, however, sensing the sign of the stored bit is destructive. In addition, high density memory devices cannot be fabricated due to the size of the ferromagnetic cores and the sense voltage becomes too small to detect as the device is miniaturized. Similarly, a plated wire memory cannot achieve high density, due to the method of fabricating the wires and decreasing sense voltages as the device is miniaturized.
Prior magnetic random access memories (MRAM) use an open magnetic structure for the sense layer. The open magnet structure, however, causes problems with write margin as the bit size is decreased.
U.S. Pat. No. 5,587,943 “Nonvolatile magnetoresistive memory with fully closed flux structure”, issued Dec. 24, 1996, and describes a memory cell, including a storage element having a first structure with a plurality of layers. Selected layers have magnetization vectors associated therewith. The first structure exhibits giant magnetoresistance (GMR), wherein the storage element has a ‘closed’ flux structure in at least one dimension, and wherein the magnetization vectors are confined to the at least one dimension during all stages of operation of the storage element. The memory cell includes a means for reading information from and writing information to the first structure and a selection conductor for applying one or more selection signals to the storage element to enable reading from and writing to the first structure. Thus, GMR is used to detect the sign of the bit. The GMR sensor interrupts the closed flux structure or the closed flux structure is entirely made up of GMR materials.
U.S. Pat. No. 5,025,416 “Thin film magnetic memory elements”, issued Jun. 18, 1991, and describes closed flux structures that are parallel to the wafer. A magnetic memory element is fabricated from a thin magnetic film wherein the magnetic film is grown on a lattice-matched substrate and subsequently patterned to form a closure domain. The closure domain is comprised of a plurality of legs that are joined at domain walls. The individual legs are patterned in the thin magnetic film to lie parallel to an easy axis of the thin film crystal structure being used. Thus, each closure domain represents a magnetic memory element.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an MRAM that has a closed flux structure that can be scaled to increase memory density.